1. Field of the Invention
This invention relates to misfire detecting systems for internal combustion engines, and more particularly to a misfire detecting system for an internal combustion engine which detects the occurrence of misfires caused by abnormal conditions in the ignition system or fuel system of the internal combustion engine.
2. Discussion of the Related Art
A misfire detecting system of this type has been disclosed, for instance, by Japanese Patent Application (OPI) No. 26345/1987 (the term "OPI" as used herein means an "unexamined published application"). The system operates as follows: The pressure in a cylinder (hereinafter referred to as "a cylinder pressure", when applicable) of the engine is detected with a cylinder pressure sensor, and a crank angle is obtained when the cylinder pressure shows a peak value. And when this peak position is in a predetermined range of crank angles, it is determined that the cylinder is in normal state.
In the case of the above-described conventional misfire detecting system, in order to detect the peak position of the cylinder pressure, it is necessary to measure the cylinder pressure continuously every predetermined crank angle or every predetermined period of time. Hence, the system is disadvantageous in that it is unavoidably intricate in arrangement. On the other hand, when the engine is operated under light load, the cylinder pressure shows two peak values; one being provided at the top dead center in the stroke of compression, and the other due to combustion, which makes it difficult to detect the occurrence of a misfire. In the case where the peak value appears before the top dead center in the stroke of compression, it is impossible to determine the occurrence of a misfire.